Corrosion inhibitors for aqueous acids



United States Patent Ofifice 3,231,507 Patented Jan. 25, 1966 3,231,507 CORROSION INHIBITORS FOR AQUEOUS ACIDS Alvin F. Beale, Jr., and Clare H. Kncera, Tulsa, Okla, assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Apr. 21, 1960, Ser. No. 23,648 9 Claims. (Cl. 252-146) This invention relates to synergistic combinations of acetylenic alcohols as corrosion inhibitors for aqueous solutions of non-oxidizing acids.

Propargyl alcohol is well known as a corrosion inhibitor. Its higher homologs also are active inhibitors. In view of this prior knowledge, it would be expected that mixtures of acetylenic alcohols such as propargyl alcohol and its homologs would exhibit additive inhibition in aqueous acids. However, it has now been discovered that mixtures of acetylenic alcohols, that is, propargyl alcohol and its homologs, are synergistically effective as corrosion inhibitors. This unexpected discovery permits the inhibition of aqeuous acid solutions by use of a smaller total amount of inhibitor than is possible when using only one of the acetylenic alcohols.

In many applications, such as metal cleaning and oil well acidizing, aqueous acids are in contact with metals at elevated temperatures. In these applications it has been found that many corrosion inhibitors that are effective at ordinary temperatures fail at the higher temperatures. Accordingly, it is common practice to evaluate inhibitors at elevated temperatures, it being known that those thus found to be effective will also be effective at lower temperatures. Likewise, it is common practice to evaluate inhibitors in 15% aqueous hydrochloric acid, since it has been found that other non-oxidizing acids give similar results and the etfect of concentration is well known; i.e., corrosion gradually increases as the acid concentration is increased, at least in the range of concentration up to The preferred acetylenic alcohols are those corresponding to the formula wherein n is an integer from 0 to about 8.

Many alcohols having the above formula are known and methods for the preparation of such compounds are likewise known. A convenient and well-known procedure for their synthesis consists of condensing the appropriate aldehyde, C H -CHO, with sodium acetylide. The preferred aldehydes are those having unbranched carbon chains, although the unexpected synergistic result is also obtained with branched chain alcohols.

To illustrate the practice of the invention and to demonstrate the synergistic corrosion inhibition effected by the compositions of the inventions, a series of standardized corrosion tests were run under controlled conditions.

Pr0cedure.The metal coupons were suspended in the acid solution containing the inhibitor for the specified time and at the specified temperature. The coupons were then removed, rinsed, dried and weighed to determine the weight of metal lost during the test. From this and the surface area of the coupon, the corrosion rate was calculated as lbs. per. sq. ft. per day. Results of same typical tests are shown in Table I.

TABLE I.-EFFECT OF VARIOUS ALKYNOLS AND MIXTURES THEREOF AS CORROSION INHIBITORS IN HYDROCI-ILORIO ACID Acid media m1. of 15% hydrochloric acid MetalAISI 1010 mild steel coupon (0.12 x 1.0" x 2.75) Temperature200 F.

Length of testi6 hours Test Concentration alkynol a (percent by volume) Corrosion Propynol Pentynol Hexynol Heptynol Decynol cooooooo o oooocno to to m ocgwwoxcn PPPPPPI'H Z'H PPPPPPZ'H Z'H cooooocaooooooo ccooooo o HUIOOOMDJ m oocnoo a Each alkynol was made by condensing sodium acetylide with the appropriate n-alkanal.

TABLE II.EFFECT OF VARIOUS CONCENTRATIONS OF THE INHIBITOR SYSTEM IN CONTROLLING ACID CORROSION Test conditionsSee Tab 1e I Inhibitor system-l part (by volume) heptynol 1 part propyn ol Concentration inhibitor Corrosion rate Test system (percent by (lbsJftfi/day) volume) Similar results are obtained with other combinations of alkynols.

While a minimum of about 0.1% of inhibitor is required for prolonged protection at elevated temperatures of the order of 200 F., much less is effective at lower temperatures or for shorter periods. Under these milder conditions, as little as 0.01% may be adequate.

Tests were made under the same conditions as those reported in Table I using an inhibitor system composed of various ratios of one alkynol containing 3 to 6 carbon atoms combined with a second alkynol containing 7 to 10 carbon atoms. It was found that synergism occurred with volume ratios varying between 15:85 to 85:15 of the two alkynols. The most pronounced effect was observed when the alkynols were present in substantially equal amounts.

Tests similar to those described above showed that the combinations of alkynols are synergistically effective as corrosion inhibitors in aqueous solutions of other acids, including sulfuric, sulfonic, phosphoric, and acetic acid; in acids of other concentrations up to at least 50%; in acids at other temperatures up to or exceeding 200 F., depending somewhat on the identity and concentration of the acid; and in the protection of other metals, including oil field tubing, cast iron, mild steel, stainless steel, admiralty metal and copper.

Effective inhibitors are obtained by mixing three or more alkynols but in general, there is little advantage in including more than two.

Best results are obtained when the inhibitor composition comprises two alkynols differing by at least 3, and preferably 4 or 5 carbon atoms. Thus, in the preferred compositions, a lower alkynol containing 3 to 6 carbon atoms is mixed with a higher one containing about 7 to 11 carbon atoms.

We claim:

1. A corrosion inhibitor composition consisting essentially of a mixture of a pair of alkynols in a volume ratio between about 15:85 and 85:15, said pair being selected from the group consisting of (a) propynol and butynol (b) propynol and pentynol (c) propynol and nonynol (d) propynol and decynol (e) butynol and decynol (f) pentynol and decynol 2. A corrosion inhibitor composition consisting essentially of asynergistic mixture of propynol and butynol in the ratio of 15;85 to 85:15 by volume.

3. A corrosion inhibitor composition consisting essentially of a synergistic mixture of propynol'and decynol in the ratio of 15:85 to 15 by volume.

4. An aqueous non-oxidizing acid containing a pair of alkynols selected from the group consisting of (a) propynol and butynol (b) propynol and pentynol (c) propynol and nonynol (d) propynol and decynol (e) butynol and decynol (f) pentynol and decynol the volume ratio of the two alkynols being between about 15 :85 and 85 :15, said pair being present in an amount sufiicient to substantially inhibit the corrosion of metals exposed to said acid.

5. A composition consisting essentially of hydrochloric acid containing about 0.01 to 0.4% by weight of a synergistic corrosion-inhibiting mixture of propynol and butynol, said mixture being in the rate of 15:85 to 85:15 by volume.

6. A composition consisting essentially of hydrochloric acid containing about 0.1 to 0.4% by weight of a synergistic corrosion-inhibiting mixture of propynol and decynol, said mixture 'being in the ratio of 15 :85 to 85: 15 by volume. v

7. The process of inhibiting the corrosion of metals in contact with aqueous, non-oxidizing acid comprising incorporating into the acid a pair of alkynols selected from the group consisting of (a) propynol and butynol (b) propynol and pentynol (c) propynol and nonynol (d) propynol and decynol (e) butynol and decynol (f) pentynol and decynol the volume ratio of the two alkynols being between about 15 :85 and 85 15, said pair being used in an amount sufficient to substantially inhibit the corrosion of said metal.

8. The process of inhibiting the corrosion of metals in contact with hydrochloric acid comprising incorporating into the acid an effective amount of about 0.01 to 0.4% by weight, based on said acid, of an inhibitor consisting essentially of a synergistic mixture of propynol and butynol in the ratio of 15 :85 to 85:15 by volume.

9. The process of inhibiting the corrosion of metals in contact with hydrochloric acid comprising incorporating into the acid an effective amount of about 0.01 to 0.4% by weight, based on said acid, of an inhibitor consisting essentially of a synergistic mixture of propynol and decynol in the ratio of 15 :85 to 85:15 by volume.

References Cited by the Examiner UNITED STATES PATENTS 2,106,181 1/1938 Kreimeier 260-638 2,613,131 10/1952 Barnes et al. 2,913,408 11/1959 Pumpelly et al. 252146 XR FOREIGN PATENTS 468,231 12/1951 Italy.

JULIUS GREENWALD, Primary Examiner.

JOSEPH R. LIBERMAN, Examiner, 

4. AN AQUEOUS NON-OXIIDIZING ACID CONTAINING A PAIR OF ALKYLNOLS SELECTED FROM THE GROUP CONSISTING OF 